Know-nothing (definition)

A member of a secret political organization in the United States, the chief objects of which were the proscription of foreigners by the repeal of the naturalization laws, and the exclusive choice of native Americans for office.

⇒ The party originated in 1853, and existed for about three years. The members of it were called Know-nothings, because they replied "I don't know," to any questions asked them in reference to the party.